This invention is directed to an electrophotographic photoreceptor. More particularly, the invention is directed to a photoreceptor having a composite interfacial layer.
The formation and development of images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The best known of the commercial processes, more commonly known as xerography, involves forming an electrostatic latent image on the imaging surface of an imaging member by first uniformly electrostatically charging the surface of the imaging layer in the dark and then exposing this electrostatically charged surface to an imagewise pattern of activating electromagnetic radiation. The light-struck areas of the imaging layer are thus rendered relatively conductive and the electrostatic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the electrostatic latent image on this image bearing surface is typically rendered visible with a finely divided colored marking material, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface which retain the electrostatic charge and thus form a visible powder image. The electrostatic latent image may also be used in a host of other ways as, for example, electrostatic scanning systems may be employed to "read" the latent image or the latent image may be transferred to other materials by TESI techniques and stored. A developed image can then be read or permanently affixed to the photoconductor where the imaging layer is not to be reused.
In the commercial "plain paper" copying systems, the latent image is typically developed on the surface of a reusable photoreceptor, subsequently transferred to a sheet of paper and affixed thereto to form a permanent reproduction of the original object. The imaging surface of the photoreceptor is then cleaned of any residual toner and additional reproductions of the same or other original objects can be made thereon.
Xerographic photoreceptors typically exhibit a reduction in potential or voltage leak in the absence of activating illumination which is known as "dark decay" and also typically exhibit a variation in electrical performance upon repetitive cycling which is known as "fatigue". The problems of dark decay and fatigue are well known in the art. They have been significantly reduced by the incorporation of an interface layer in the photoreceptor between the conductive substrate and the photoconductive insulating layer. Many materials, both organic and inorganic, which are suitable for use in the interface are known in the art. See, for example, U.S. Pat. No. 2,901,348.
In addition to the electrical requirements of such interface layers, it is also necessary that they meet certain requirements with regard to mechanical properties such as adhesion of the photoconductive layer thereto and, depending upon the type of imaging member, overall flexibility in some instances. For example, when using a flexible photoreceptor such as a continuous belt, the photoconductive insulating layer and the interface layer should be properly matched so as to have the required electrical and mechanical stability. Some interface layers tend to spall or crack after repeated flexing thus resulting in sections of the photoconductive layer flaking off or spalling thereby rendering it no longer suitable for use.
Many compositions, both organic and inorganic, are known for use as interface materials in photoreceptors. Nevertheless, as the art of xerography has advanced and more stringent demands are imposed upon the photoreceptor because of increased performance standards such as, for example, speed of operation, flexibility requirements, etc., there is a continuing need for new and improved interface structures which meet both the required electrical and mechanical properties for use in particular applications. The present application relates to a photoreceptor having a novel composite interface structure.